Question

докажите равенство:
cos 48 + sin 18 - cos 12 = 0

Answer 1

cos 48 = sin 42, cos 12 = sin 78
sin 42 + sin 18= sin 78
formula: sinx + sin y = 2. sin(x+y)/2.cos (a-b)/2
sin 42 + sin 18 = 2.sin 30 .cos 12= 2.1/2.cos 12=cos 12 = sin 78

(sin (90-x) =cos x)